Crystal production



n. w. Moons, CRYSTAL PRODUCTION.

APPLICATION FIL'ED FEB. 26. |918.

'Patented July 20,` l1920.

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Inventor Rog `W. moore,

,UNIT-ED! STATES l` ROY MOORE, OF SCHENECTADY, NEW' YORK,l ASSIGNOR TOGENERAL COMPANY, A CORPORATION OIF NEW YORK.

PATENT' OFFICE.-

cnYsrAr. PBonUc'rIoN.

Application, led February To all lwhom it may concern.'

Beit known that I, ROY W. MooRE, a citizen of the rUnited States,residing at Sche-` nectady, in thecounty of Schenectady, State of NewYork, have invented certain new' andusefulImprovements in CrystalProduction, of which the following is a speellication.

The present invention comprises a method vof and apparatus for growingclear crystals;

1n other words, crystals having a uniform orlentation.

According to one method' whereby large fragments could be thus produced.This procedure is not suited, however, for the proi Vduction ofstructurally uniform crystals of large size even when so favorable amaterial as alum crystallized. A

`,have found that crystals of various sub-I stances can be produced ofgreater size and erfectionA than heretofore by controlling oth thetemperature and the evaporationA of thelsolition or mother liquor toproduce and maintain by such control a slight 'degree of supersaturationin the solution which I lhave found` to be favorable for regularcrystal-- lization. By'carefully maintaining the degree 'ofsupersaturation below the point of.

irregular crystallization, perfectly developed clear crystals of largesize may be formed which continue to grow clear and perfect as long as asuitable state of supersaturation is maintained. y, l

Y In the accompanying drawing' Figure 1 is a vertical section of oneform of apparatus AGI for carrying out my invention; Fig.- 2 illustratesa modified-apparatus.; Fig. 3 1s acurve expressing the 1 relation lbetween lspecific gravity and saturation temperature of a solution, andFigui is a perspective view of 'l a crystal produced by my new method.

Accodingto the preferred methodl of -car'rying out my invention fontheproduction of large cr stals ofa chosen material, for example, ofochelle salt (sodlum potas- ,J sium tartrate), a saturated ,solution ofthe salt is made up at some convenient temperaspecification u: LetterslPatent( Patentd ,July 20, 1920 2.6, 1918. Serial Nol 219,312.

ture, ffor example, at aboutl 32 to 35 C. ,After the solution hasbeenremoved from to about I to 8 C. above the saturation temperature and thesolution is ltered. In

some lcases the' solution is thereupon 'subjected to a vacuum in orderto remove dissolved air but this is not absolutely necessary. Beforecrystallization involving exact temperature control, it is Inecessary toknow exactly at what temperature asgiven solution will begin tocrystallize: Although thismight be determined by trial for a givenconcentration and this concentration tliereafterreproduced, it is moreconvenient to proceed as follows: Y

A The specific gravity ofv solutions of a given substance is determinedat various temperatures over a range of temperatures, say, five degreesapart, and the results are plotted as a curve. For example, Fi 3illustrates a curve thus obtained with -ochelle salt, the ordinatesrepresentthevspeciic gravity as determined by a hydrometer and theabscissae the corresponding temperatures.. From this curve thetemperature o f'saturation of a solution may be found by determining thespecific gravity, allowance 'being made for the fact that the specificgravity is deter- 'mined at la temperature somewhat above-thevsaturation temperature. The specific grav- 1ty changes about 0.0005 fora change'of one .degree in temperature.

When readyfor crystallization the solution is introduced into ajar 1.located within av tank 2 provided with a cover 3. Within ELECTRIC theexcess of salt, the temperature is raised say the tank 2 and around thejar 1 is a suitable bath 4, such as water which serves as a 'heatreservoir in order te stabilize the temperature of the solutionin whichcrystal growth is to be produced. Inlsuitable thermal relation to theheat reservoir for example, surrounding the tank 2 as illustrated, is anelectric resistance heater 5. The tank is well heat-insulated, forexample, by a surroundingl layer of felt 6or other suitable materiaCrystallization may be begun in this solution spontaneously by simplylowering the temperature as will be hereinafter described, but I preferto start crystallization upon Asomecrystalline particles 7 suspended bya Afine thread or very fine wire 8 from supports 9, which convenientlymay consi..t of glass rods. These crystalline particles or yseedcrystals consist preferably of small crystals or crystal fragments ofthematerial to be crystallized, but they.may also consist of small crystalsor crystal fragments of someY other material which is isomorphous withlthe material to be crystallized. Preferably these crystal fragments arehung in zones at different heights from the bottomof the receptacle l,and preferably a shield -10 `of glass, or other suitable materiaL-isplaced ,Y upon the supports 9 above the seed crystals to protect thegrowing` crystals from 'chance crystals which' form spontaneously in thesolution. The jar 1 preferably is covered with a plate l1.

When using about eight to ten liters of solution from which to growcrystals, I

`prefer to place into the solution about fifteen seed crystals hunginthree zones and located apart as far as practicable. 1f more than thisnumber are grown the crystals are likely to come into Icontact as theyincrease in size therebyv causing defects. vA smaller number of crystalsof course will enable crystals to be grown to larger size, but Cthe-`rate of growth should be slower. y

The temperature of the bath 4 in the tank i '2 should be about 0.50above the saturation temperature of the solution in the jar 1.

The temperature of the apparatus after being assembled, as abovedescribed, is allowed to fall to practically the saturation tempera.`

--such, for example, as shown in the drawing.'

This thermostat consists of a bulb 12 containing mercury whichcommunicates with a tube 13. Electrical contact to the mercury in thebulb 12 is made by means of a wire 14 sealed into`the Wall of the bulb.The

bore/of tube 13 containing the mercury column, is of capillarydimension. rThe upper part of the bore is somewhat wider, and contalns afine wire 15 connected to a screwthreaded lrod 16. Upon thisscrew-threadedv rod is a rotatablenut 17 by the rotation of' which thescrew-threaded rod is raised or lowered. When the water b ath is at adesired temperature of saturation, which can accurately be determined bya sensitive thermometer, the sleeve 17 is adjusted so that the.electrical contactis made by the wire( 15v to the` mercury thread in thecapillary tube l2. The iod `16 and the conductor. 13 are connected to arelay circuit containing a battery 19 and a. relay magnet 20. Themovable contact 2l of this relay circuit coperates with stationarycontacts 22 so asV to open and close by its movements the heater circuit23. lnthis circuit 2?;is a suitable source of electrical energy, such asa generator 24 which may also be switched in and out of circuit with amanually operated switch 251.

When the temperature ofthe apparatus falls a few hundredths of a degreeContact between the Wire 15 and the mercuryvthread in the tube 13 isinterrupted causing the relay. magnet 20 to release its armature andclose the heater circuit, thereupon raising thetemperature ofthe'apparatus until the vcontact of the mercury thread and the wire 15is restablished'. By this means the temperature is maintained constantwithin about 0.050, C. It is to be understood that the describedthermostat is shown for the purpose of illustration only and any-othersuitable means for accurately controlling the temperature may beemployed.

When xthe apparatus is adjusted and functionates properly at thesaturation temperature the thermostat setting is changed to lower thetemperature'0-l0 C. to produce a \slight supersaturation and therebycausing growth of the seed crystals. As the growth of crystal orcrystals in the solution'withdraws some of the material from solution,the favorable degree of Isupersaturation must be maintained andpreferably this is done by reducing the temperature.

After increase in size of the seed crystals has become noticeable, thethermostat is adjusted to permit a fall of temperature of about 0.20 C.4per day. rlhe setting is changed 0.10 CJ about every twelve. hours.

After the crystals have increased to a size three-fourths inch to oneinch in length, the ltemperature of the bath may fall about 0.3 to 0.40per day,",and when the crystals are well over one inch in length thedecrease in temperature may be 0.50 to 0.60 per day, the setting of thethermostat being changed twice ea'ch day. When the solution has cooledto about roomtemperature the crystals are remoyed from the mother liquorand are dried by wiping with a soft, dry-cloth.

A. crystal 27 of Rochelle salt is shown in Fig. 4, built up about thenuclear crystal 7, but it should be understood that the size of thecrystal in the drawing is of no significance as vlarger crystalsmay begrown than represented in the drawing.

`1n some cases the crystals may be grown l by placing the seed crystalson glass plates so as to avoid the use of suspension thread, and whilethe crystalsl will row clear and uniformly under these conditions 'theresulting large crystals are only partially developed as thesideadjacent the glass does not developf 1n some cases clear, perfectcrystals of fair size will develop from chance tions.

J crystallization under the described. condiln some cases, as shown inFig. 2, the de gree of supersaturation of the solution mayM becontrolled by maintaining thetemperature constant and controlling theevaporation. For this purpose the solution may be placed in a j ar lcontaining a tightly fitting and velocity of the gas stream, the volumeof the solution and the character of the material to be crystallized, noexact directions can be given other than to saythat the evaporationshould loccur at such rate that the favorable supersaturation ismaintained without causing-it tovproceed so far as to cause irregularcrystallization. The temperature of the bath 4 surrounding the ar 1 ismaintained constant by a thermostat as shown in` Fig. 1.- The setting ofthe thermostat may either remain unchanged, or may be changed vapredetermined amount to lower the temperature coincident with theevaporation-of the solvent. A single crystal 31'suspended from a support32, resting on a standard 33 'has been shown as developing the apparatusillustrated by Fig. 2 but, of course, a greater number may begrown asshown in Fig. 1.

Crystals made in accordance with my invention are of particular utilityin scientific apparatus, utilizing theAPiezo-electric effect.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. The method of producing crystals which consists in producingsupersaturation in a solution of the material to be crystallized,maintaining said solution supersaturated when crystallization has begunbut -holding the degree of supersaturation ofsaid solution below thepoint at which crystallization occurs.

irregular l2. The method of producing regular crystals which consists inproduclng supersaturation in a solution of a material to be crystallizeduntil crystallization begins, fand lowering the temperature at a rate ofless than onedegree per day to maintain said solution lto becrystallized, producing supersaturation in said solution until crystalgrowth occurs, and v lowering the temperature at a rate adapted tomaintain concentration at 'the point at which regular crystallizationoccursl around said yparticle as the concentration of the solutiondecreases.

Il. Tl`hey method of producing regular crystals which consists inplacing a crystalline particle of the 'materiallto be crystallized intoa nearly saturated solution of said material, substantially preventingevaporation ofsolvent from said solution, controllably lowering thetemperature of said solution at a rate which will producesupersaturation suiiicient to induce regular Icrystal growth upon saidparticle Vas a nucleus while preventing a degree of supersaturationwhich will produce irregular crystallization.

5. The method of growing crystals which consists in placing in contactwith a nearly saturated solution of the lmaterial lto be crystallized,acrystalline particle which is isomorphous with said material, producingsupersaturation `in said solution and controllably heating and coolingthe solution as the concentration decreases/due to crystalline growth toprogressively lower the temperature ata rate adapted-to maintain a de- Isired supersaturation favorable for crystal growth on said particle butbelow the point at which irregular crystallization occurs. 6. The methodof producing crystals which consists in placing into contact with asolution of the material to be crystallized a crystalline particle whichis isomorphous with said material, substantially preventing evaporationof the solvent from said solution, producing supersaturation andmaintainin the `degree of supersaturation thereof wit in the limits atwhich crystal growth occurs by a progressive lowering of temperature ata rate which will prevent the supersaturation to become great enough tocause irregular crystal formation.

7. The method'of producing regular crystals which consists in placing acrystalline particle of the material to be crystallized into a solutionhavinga temperature several degrees above the saturation temperature forthe given concentration, substantially y preventing evaporation ofsolvent from said solution, lowering the ,temperature to substantiallythe turation temperature, thereafter loweringthe temperature about 0.1oC.

gradually increasing the rate-of cooling as. `v

the size of' the crystal increases.

8. The'method of producing large clear crystals of Rochelle salt whichconsists in placing a crystalline particle of saidsalt in contact with anearlyl saturated solution of said salt, producing supersaturation ofsaid solution by loweringthe temperature until crystal growth takesplace on said particle causing the cooling of said solution to occur atsuch rate that yexcessive supersaturation is i 'In witness whereof, Ihave hereunto'set my hand this 25th day of February, 1918. ROY W. MOORE,

' and preventing irregular crystallization by A 110 per day untilnoticeable crystal growth onV said particle has taken place, andthereupon`

